The present invention relates to: a method of preparing a capstock layer that includes a comb copolymer; a method of preparing a multi-layered polymeric composite, one layer of which is a capstock layer; and a capstock layer and a multi-layered polymeric composite formed, respectively, thereby.
The thermoplastic polymer, poly(vinyl chloride) (xe2x80x9cPVCxe2x80x9d) has a combination of properties which make it particularly suitable for use as a structural material. In applications in which impact strength of the structural plastic is important, the PVC can be formulated with impact-modifier resins which improve the impact strength of the resulting composition. Such high impact-strength PVC compositions can be readily extruded or otherwise formed into a variety of articles which have excellent impact strength, toughness and other desired mechanical and chemical properties; for example as siding for buildings, shutters, technical profiles for window and door frames, rain carrying systems (e.g., gutters and downspouts), and fencings.
Such PVC compositions however have relatively poor weatherability characteristics, particularly poor color retention in darker grade colors such as browns and blues. The color is imparted to the PVC composition, for instance, by the use of colorants such as pigments or dyes, but exposure to sunlight causes unappealing changes in the colors. Such unappealing changes are more severe for darker than for light colors. Poor weatherability characteristics also cause reduction in impact strength leading to embrittlement and cracking and/or mechanical failure of the articles prepared from such compositions. Thus, there is a need for improving the weathering characteristics of such materials.
One remedy has been to incorporate stabilizing additives into the PVC composition, for example UV absorbers, thermal stabilizers and titanium dioxide light scatterer. However, the resulting improvements to weatherability are still not sufficient to meet the new, stricter industry-wide standards (Vinyl Siding Institute, January 1999, adopting ASTM D3679 performance specifications).
Another attempted remedy has been to apply another resinous material over the PVC to provide a surface that can withstand sunlight and other environmental conditions. Such a surfacing material is called a xe2x80x9ccapstockxe2x80x9d. The capstock layer generally is much thinner than the thermoplastic substrate layer, typically being about 5 to about 25% of the total thickness of the composite (i.e. the capstock layer and substrate layer).
A suitable capstock material must possess a certain combination of processing properties and other physical, chemical, and aesthetic properties, including exceptional weathering characteristics such as excellent color retention and high impact strength. Moreover, the capstock also must not adversely affect those properties which make PVC such a widely used building material. In particular, the capstock compositions that are particularly aesthetically desirable do not have a shiny appearance but rather have a flat, or reduced gloss appearance.
Various types of polymer-based compositions have been disclosed for use as capstock, including PVC-based compositions and acrylic resin based compositions. A number of these polymer-based compositions are disclosed in European Patent Application EP-A-473,379. This publication discloses a capstock composition containing a blend of PVC resin and an acrylic copolymer. We have found, however, that the presence of PVC in capstock compositions such as those disclosed in EP-A-473,379 results in reduced weatherability and high gloss.
EP-A-1,061,100 discloses a capstock composition that contains a particular combination of xe2x80x9chigh rubber corexe2x80x9d and xe2x80x9cmedium rubber corexe2x80x9d acrylic-based xe2x80x9ccore/shellxe2x80x9d polymers and is capable of providing the requisite impact strength, high color retention, and reduced gloss without requiring additional PVC or flatting agents. Unfortunately, this approach is a macroscopic blend approach requiring a processing blend step which is undesirable from an economic point of view. Moreover, because the macroscopic blend approach produces macroscopic domains having sizes on the order of the wavelength of visible light, physical stressing of the capstock layer can be very deleterious to the appearance of the capstock layer, and to the appearance of the composite as a whole. Physical stressing by, for example, bending, creasing, or impact events caused pronounced whitening (so called xe2x80x9cstress whiteningxe2x80x9d) at the point of stress.
Thus there is a need for a cost-effective, weatherable, capstock material having a high impact strength, adequate color retention, and resistance to crease or stress whitening.
We have, surprisingly, found that the comb copolymer of the present invention can be melt processed to form a capstock melt layer that can be contacted with a substrate melt layer to form a multi-layered polymeric composite in which the capstock layer displays superior weatherability, impact resistance, other mechanical properties, and stress whitening resistance, and which is capable of protecting the substrate layer from damage associated with weathering and other environmental stress, including impact events.
One aspect of the present invention relates to a composition comprising a comb copolymer:
wherein said comb copolymer comprises a backbone and at least one graft segment; and
wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of xe2x88x9265xc2x0 C. to 10xc2x0 C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180xc2x0 C.
A second aspect of the present invention relates to a process comprising the steps of:
(a) forming a capstock composition;
(b) feeding said capstock composition into an extruder comprising a feed section and a metering section;
(c) metering and melting said capstock composition to form a capstock melt;
(d) forming said capstock melt into a capstock melt layer;
(e) extruding said capstock melt layer; and
(f) cooling said capstock melt layer to form a solid capstock layer;
wherein said capstock composition comprises a comb copolymer comprising a backbone and at least one graft segment; and wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of xe2x88x9265xc2x0 C. to 10xc2x0 C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180xc2x0 C.
A third aspect of the present invention relates to a coextrusion process comprising the steps of:
(A) forming a capstock melt layer by a process comprising the steps of:
(a) forming a capstock composition;
(b) feeding said capstock composition into a first extruder comprising a feed section and a metering section;
(c) metering and melting said capstock composition to form a capstock melt;
(d) forming said capstock melt into a capstock melt layer; and
(e) extruding said capstock melt layer;
wherein said capstock composition comprises a comb copolymer comprising
a backbone and at least one graft segment; and wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of xe2x88x9265xc2x0 C. to 10xc2x0 C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180xc2x0 C.
(B) forming a substrate melt layer by a process comprising the steps of:
(a) forming a substrate composition;
(b) feeding said substrate composition into a second extruder comprising a feed section and a metering section;
(c) metering and melting said substrate composition to form a substrate melt;
(d) forming said substrate melt into a substrate melt layer;
(e) extruding said substrate melt layer; and
wherein said substrate composition comprises a thermoplastic polymer;
(C) causing said capstock melt layer to contact said substrate melt layer to form a multi-layered melt composite; and
(D) cooling said multi-layered melt composite to form said multi-layered polymeric composite, comprising a solid capstock layer disposed upon a solid substrate layer.
A fourth aspect of the present invention relates to a multi-layered polymeric composite comprising:
(a) at least one solid substrate layer comprising a thermoplastic resin; and
(b) at least one solid capstock layer disposed thereon, wherein said solid capstock layer comprises a comb copolymer:
wherein said comb copolymer comprises a backbone and at least one graft segment; and
wherein:
(i) said graft segment and said backbone are in a weight ratio from 30:70 to 60:40;
(ii) said backbone is immiscible with said graft segment at room temperature;
(iii) said backbone has a glass transition temperature of xe2x88x9265xc2x0 C. to 10xc2x0 C.; and
(iv) said graft segment has a glass transition temperature of 60 to 180xc2x0 C.
In yet another aspect, the thermoplastic polymer is a polymer selected from the group consisting of poly(vinyl halide), chlorinated poly(vinyl chloride), ABS terpolymer, polyaromatics including high impact polystyrene (HIPS), polyamides, polyesters, polyolefins including polypropylene, and combinations thereof.
In a still further aspect, the solid capstock layer of the multi-layered polymeric composite has an impact resistance energy of at least 2 joules.
Used herein, the following terms have these definitions:
The xe2x80x9cbackbonexe2x80x9d of a polymer chain is a collection of polymerized monomer units attached to one another. The attachment is typically achieved by covalent bonding. xe2x80x9cNon-terminalxe2x80x9d monomer units are directly attached to at least two other monomer units. A xe2x80x9cterminalxe2x80x9d monomer unit resides at the end of the polymer chain and is directly attached to one other monomer unit. For example, the polymerized monomer units of the backbone may be derived from ethylenically unsaturated monomers. It is required that the composition of the backbone of the comb copolymer of the present invention will be such that the backbone is not miscible with the graft segment of the invention at room temperature. Miscibility between graft segment and backbone may, however, occur at elevated temperature, and in some cases may even be desirable. The solubility parameters of the backbone and the thermoplastic polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen, described herein below.
A xe2x80x9clinearxe2x80x9d polymer (homopolymer or copolymer) is a polymer having a backbone that is not branched. As used herein, the term xe2x80x9clinearxe2x80x9d is also meant to include polymers wherein a minor amount of branching has occurred. For example, hydrogen abstraction may lead to branching during free radical polymerizations.
A xe2x80x9cbranchedxe2x80x9d polymer is a polymer having a first xe2x80x9cbackbone segmentxe2x80x9d that has other backbone segments (i.e., xe2x80x9cbranchesxe2x80x9d) chemically attached to it through a xe2x80x9cnon-terminalxe2x80x9d atom of the first backbone segment. Typically, this first backbone segment and all of the branches have the same, or similar, composition.
A xe2x80x9cpendantxe2x80x9d group is a group that is attached to the backbone of a polymer. The term pendant may be used to describe a group that is actually part of a polymerized monomer unit. For example, the hydroxyethyl group of a polymerized unit of 2-hydroxyethyl methacrylate may be referred to as a xe2x80x9cpendant hydroxyethyl groupxe2x80x9d, or as xe2x80x9cpendant hydroxy functionalityxe2x80x9d. It is also common to refer to large groups attached to a polymer backbone as xe2x80x9cpendantxe2x80x9d when those large groups are compositionally distinct from the backbone polymer. These large groups may themselves be polymer chains. For example, when a macromonomer becomes incorporated into a polymer chain by reaction with other monomers, the two carbons of its reactive double bond become part of the backbone, while the polymeric chain originally attached to the double bond of the macromonomer becomes a xe2x80x9cpendant groupxe2x80x9d that may, for example, have a molecular weight of 1,000 to 100,000. A xe2x80x9cpendantxe2x80x9d group may further be described as xe2x80x9cpendant toxe2x80x9d the backbone.
A xe2x80x9cterminalxe2x80x9d group resides at the end of the polymer chain and is chemically attached to a terminal monomer unit. A terminal group may, for example, have a composition distinct from the composition of the backbone of the polymer. A xe2x80x9cpendantxe2x80x9d group may occur in a xe2x80x9cterminalxe2x80x9d position. As such, a xe2x80x9cterminalxe2x80x9d group is a special case of a xe2x80x9cpendantxe2x80x9d group.
A xe2x80x9cmacromonomerxe2x80x9d is any low molecular weight water-insoluble polymer or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By xe2x80x9cwater-insolublexe2x80x9d it is meant having a water solubility of no greater than 150 millimoles/liter at 25xc2x0 C. to 50xc2x0 C. By xe2x80x9clow molecular weightxe2x80x9d it is meant that the macromonomer has a degree of polymerization preferably from 10 to 1000, more preferably from 20 to 1,000, and more preferably from 40 to 200. By xe2x80x9cdegree of polymerizationxe2x80x9d it is meant the number of polymerized monomer units present in the macromonomer. See e.g., Kawakami in the xe2x80x9cEncyclopedia of Polymer Science and Engineeringxe2x80x9d, Vol. 9, pp. 195-204, John Wiley and Sons, New York, 1987. Typically, the macromonomer polymer chain contains ethylenically unsaturated monomers, as polymerized units. Preferably, the ethylenically unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein.
The term xe2x80x9cmacromonomer aqueous emulsionxe2x80x9d is used herein to describe an aqueous emulsion containing macromonomer dispersed therein as water insoluble particles.
A xe2x80x9cgraft segmentxe2x80x9d is a polymer chain occupying a pendant position along the polymer backbone. A graft segment may include, as polymerized units, one type of monomer or more than one type of monomer. The composition of a graft segment is different from the composition of the backbone polymer to which it is attached, in contrast to a xe2x80x9cbranch segmentxe2x80x9d of a branched backbone which has a composition which is the same as, or similar to, other portions the branched backbone of which it is a part. A xe2x80x9cterminal graft segmentxe2x80x9d resides at an end of a backbone polymer chain and is chemically attached to that backbone polymer chain. A xe2x80x9cterminal graft segmentxe2x80x9d is a special case of a xe2x80x9cpendant graft segmentxe2x80x9d.
xe2x80x9cGraft copolymersxe2x80x9d are macromolecules formed when polymer or copolymer chains are chemically attached as side chains to a polymeric backbone. Those side chains are the xe2x80x9cgraft segmentsxe2x80x9d described herein above. Because graft copolymers often chemically combine unlike polymeric segments in one macromolecule, these copolymers have unique properties compared to the corresponding random copolymer analogues. These properties include, for example, mechanical film properties resulting from thermodynamically driven microphase separation of the copolymer, and decreased melt viscosities resulting in part from the segmental structure of the graft copolymer, and from separation of a soft (i.e., low Tg) phase. With respect to the latter, reduced melt viscosities can advantageously improve processability of the polymer. See e.g., Hong-Quan Xie and Shi-Biao Zhou, J. Macromol. Sci.-Chem., A27(4), 491-507 (1990); Sebastian Roos, Axel H. E. Muller, Marita Kaufmann, Werner Siol and Clenens Auschra, xe2x80x9cApplications of Anionic Polymerization Researchxe2x80x9d, R. P. Quirk, Ed., ACS Symp. Ser. 696, 208 (1998).
The term xe2x80x9ccomb copolymer,xe2x80x9d as used herein, is a type of graft copolymer, wherein the polymeric backbone of the graft copolymer is linear, or essentially linear, and each side chain (graft segment) of the graft copolymer is formed by a xe2x80x9cmacromonomerxe2x80x9d that is grafted to the polymer backbone. The comb copolymers may, for example, be prepared by the free radical copolymerization of macromonomer with conventional monomer (e.g., second ethylenically unsaturated monomer).
A xe2x80x9ccomb copolymer segmentxe2x80x9d is a segment selected from the group consisting of the xe2x80x9cbackbonexe2x80x9d of a comb copolymer and the xe2x80x9cgraft segmentxe2x80x9d of a comb copolymer. It is preferred that graft segment of the present invention is miscible with the substrate polymer of the present invention. It is further required that the backbone of the comb copolymer not be miscible with the graft segment at room temperature. It is still further preferred that the backbone of the comb copolymer of the present invention not be miscible in the substrate polymer. The solubility parameters of a given copolymer segment and the substrate polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen described herein below.
A xe2x80x9csubstrate polymerxe2x80x9d is a polymer to which the capstock layer is affixed and adhered.
An xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d is an aqueous medium in which are dispersed a plurality of particles of segmental copolymer. Used herein, an xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d is an xe2x80x9caqueous copolymer compositionxe2x80x9d.
xe2x80x9cTgxe2x80x9d is the xe2x80x9cglass transition temperaturexe2x80x9d of a polymeric phase. The glass transition temperature of a polymer is the temperature at which a polymer transitions from a rigid, glassy state at temperatures below Tg to a fluid or rubbery state at temperatures above Tg. The Tg of a polymer is typically measured by differential scanning calorimetry (DSC) using the mid-point in the heat flow versus temperature transition as the Tg value. A typical heating rate for the DSC measurement is 20 Centigrade degrees per minute. The Tg of various homopolymers may be found, for example, in Polymer Handbook, edited by J. Brandrup and E. H. Immergut, Interscience Publishers. The Tg of a polymer is estimated by using the Fox equation (T. G. Fox, Bull. Am. Physics Soc., Volume 1, Issue No. 3, page 123 (1956)).
xe2x80x9cEffective Tgxe2x80x9d. When a substance having some degree of solubility in a polymer is imbibed by that polymer, the softening temperature of the polymer decreases. This plasticization of the polymer can be characterized by measuring the xe2x80x9ceffective Tgxe2x80x9d of the polymer, which typically bears an inverse relationship to the amount of solvent or other substance contained in the polymer. The xe2x80x9ceffective Tgxe2x80x9d of a polymer containing a known amount of a substance dissolved within is measured just as described above for xe2x80x9cTgxe2x80x9d. Alternatively, the xe2x80x9ceffective Tgxe2x80x9d may be estimated by using the Fox equation (supra), assuming a value for Tg (e.g., the freezing point) of the solvent or other substance contained in the polymer.
Molecular Weight. Synthetic polymers are almost always a mixture of chains varying in molecular weight, i.e., there is a xe2x80x9cmolecular weight distributionxe2x80x9d, abbreviated xe2x80x9cMWDxe2x80x9d. For a homopolymer, members of the distribution differ in the number of monomer units which they contain. This way of describing a distribution of polymer chains also extends to copolymers. Given that there is a distribution of molecular weights, the most complete characterization of the molecular weight of a given sample is the determination of the entire molecular weight distribution. This characterization is obtained by separating the members of the distribution and then quantitating the amount of each that is present. Once this distribution is in hand, there are several summary statistics, or moments, which can be generated from it to characterize the molecular weight of the polymer.
The two most common moments of the distribution are the xe2x80x9cweight average molecular weightxe2x80x9d, xe2x80x9cMwxe2x80x9d, and the xe2x80x9cnumber average molecular weightxe2x80x9d, xe2x80x9cMnxe2x80x9d. These are defined as follows:
Mw=xcexa3(WiMi)/xcexa3Wi=xcexa3(NiMi2)/xcexa3NiMi 
Mn=xcexa3Wi/xcexa3(Wi/Mi)=xcexa3(NiMi)/Ni 
where:
Mi=molar mass of ith component of distribution
Wi=weight of ith component of distribution
Ni=number of chains of ith component
and the summations are over all the components in the distribution. Mw and Mn are typically computed from the MWD as measured by Gel Permeation Chromatography (see the Experimental Section).
xe2x80x9cParticle sizexe2x80x9d is the diameter of a particle.
The xe2x80x9caverage particle sizexe2x80x9d determined for a collection of particles (e.g., macromonomer particles, or particles of graft copolymer) the xe2x80x9cweight average particle sizexe2x80x9d, xe2x80x9cdwxe2x80x9d, as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector.
The term xe2x80x9cparticle size distributionxe2x80x9d and the acronym xe2x80x9cPSDxe2x80x9d are used interchangeably. xe2x80x9cPolydispersityxe2x80x9d is used in the art as a measure of the breadth of the PSD. Used herein, xe2x80x9cpolydispersityxe2x80x9d is a description of the distribution of particle sizes for a plurality of particles. As such, xe2x80x9cpolydispersityxe2x80x9d and xe2x80x9cPSD polydispersityxe2x80x9d are used interchangeably. PSD polydispersity is calculated from the weight average particle size, dw, and the number average particle size, dn, according to the formulae:
PSD Polydispersity=(dw)/(di), 
where
dn=xcexa3nidi/xcexa3ni 
dw=xcexa3nididi/xcexa3nidi, and
where ni is the number of particles having the particle size di.
Estimation of whether a polymer and another component (i.e., another polymer of a solvent) will be miscible may be made according to the well-known methods delineated in D. W. Van Krevelen, Properties of Polymers, 3rd Edition, Elsevier, pp. 189-225, 1990. For example, Van Krevelen defines the total solubility parameter (xcex4t) for a substance by:
xcex4t2=xcex4d2+xcex4p2+xcex4h2, 
where xcex4d, xcex4p, and xcex4h are the dispersive, polar, and hydrogen bonding components of the solubility parameter, respectively. Values for xcex4d, xcex4p, and xcex4h have been determined for many solvents, polymers, and polymer segments, and can be estimated using the group contribution methods of Van Krevelen. For example, to estimate whether a polymer having a given composition will be miscible with a particular solvent, one calculates xcex4t2 for the polymer and xcex4t2 for the solvent. Typically, if the difference between the two, xcex94xcex4t2, is greater than 25 (i.e., xcex94xcex4t greater than 5), then the polymer and the solvent will not be miscible.
If, instead, it is desired to determine whether two polymers, differing in composition, will be miscible, the same calculations may be carried out, but the predicted upper limit of xcex94xcex4t2 for miscibility will decrease as the molecular weight of one or both of polymers under consideration increases. This decrease is thought to parallel the decrease in entropy of mixing which occurs as the molecular weight of the components being mixed increases. For example, two polymers, each having a degree of polymerization of 100, will likely be immiscible even if the value of xcex94xcex4t2 for their mixture is 9, or even 4 (i.e., xcex94xcex4t=3, or even 2). Still higher molecular weight polymers may be immiscible at even lower values of xcex94xcex4t. To estimate whether a graft segment of the copolymer of the present invention, having a given composition, will be miscible with a backbone having another composition, one calculates xcex4t2 for the graft segment and xcex4t2 for the backbone. Typically, if the difference between the two, xcex94xcex4t2, is greater than 9 (i.e., xcex94xcex4t greater than 3), then the graft segment should be insoluble in the backbone polymer such that a film formed by the graft copolymer would have two distinct types of polymeric phase. Similar calculation can be performed to determine whether a graft segment of a particular composition will be miscible with a thermoplastic polymer of a given composition. Similar calculation can also be performed to determine whether a backbone of a particular composition will be immiscible with a thermoplastic polymer of a given composition.
Used herein, a xe2x80x9csolid capstock layerxe2x80x9d of the present invention having a composition identical to the composition of Dropping Dart Impact specimens, prepared and tested according to dropping dart impact resistance test ASTM method D-446 with impact head configuration H.25, will be referred to as having a value for impact resistance energy equal to the value for impact resistance energy determined for those Dropping Dart Impact specimens. A solid capstock layer is herein considered to be impact resistant if the corresponding Dropping Dart Impact specimens having the same composition exhibit dart impact energy (average of ten specimens) of at least 2.0 joules. Preferably, the dart impact energy is 3.0 joules to 9.0 joules, more preferably 4.5 to 9.0 joules, and most preferably 5 to 8 joules.
A preferred method of preparing the graft copolymers of the present invention and their aqueous dispersions is by emulsion polymerization. A preferred process for this preparation includes (a) forming, by polymerization of at least one first ethylenically unsaturated monomer, a macromonomer aqueous emulsion containing one or more water-insoluble particles of macromonomer; (b) forming a monomer composition containing at least one second ethylenically unsaturated monomer; and (c) combining at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition to form a xe2x80x9cpolymerization reaction mixturexe2x80x9d. The macromonomer and second ethylenically unsaturated monomer are polymerized in the presence of an initiator to form graft copolymer particles. The graft copolymers prepared by this preferred process are comb copolymers.
The macromonomer, present in the macromonomer aqueous emulsion as water insoluble particles, is any low molecular weight water-insoluble polymer or copolymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process. By xe2x80x9cwater-insolublexe2x80x9d it is meant having a water solubility of no greater than 150 millimoles/liter at 25xc2x0 C. to 50xc2x0 C. By xe2x80x9clow molecular weightxe2x80x9d it is meant that the macromonomer, typically, has a degree of polymerization of 10 to 2,000, preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 40 to 200. By xe2x80x9cdegree of polymerizationxe2x80x9d it is meant the number of polymerized monomer units present in the macromonomer.
The macromonomer contains, as polymerized units, at least one first ethylenically unsaturated monomer. Preferably, the first ethylenically unsaturated monomer is selected to impart low or no water solubility to the macromonomer as previously described herein.
It is preferred, though not required, that the composition of the macromonomer be chosen such that the graft segments of the comb copolymer formed therefrom will be miscible in the substrate polymer of the invention. The solubility parameters of the macromonomer (and graft segment prepared therefrom) and the substrate polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen, described herein above.
The composition of the macromonomer should be chosen so that the Tg of the graft segment of the comb copolymer formed therefrom will be preferably from 60xc2x0 C. to 180xc2x0 C., more preferably from 70xc2x0 C. to 130xc2x0 C., and most preferably from 80xc2x0 C. to 120xc2x0 C.
Suitable first ethylenically unsaturated monomers for use in preparing macromonomer include for example methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, stearyl methacrylate; acrylate esters, such as C1 to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene; olefinically unsaturated nitrites, such as acrylonitrile or methacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate; N-vinyl compounds such as N-vinyl pyrrolidone; acrylamide; methacrylamide; substituted acrylamides; substituted methacrylamides; hydroxyalkylmethacrylates such as hydroxyethylmethacrylate; hydroxyalkylacrylates; basic substituted (meth)acrylates and (meth)acrylamides, such as amine-substituted methacrylates including dimethylaminoethyl methacrylate, tertiary-butylaminoethyl methacrylate and dimethylaminopropyl methacrylamide and the likes; dienes such as 1,3-butadiene and isoprene; vinyl ethers; or combinations thereof. The term xe2x80x9c(meth)xe2x80x9d as used herein means that the xe2x80x9cmethxe2x80x9d is optionally present. For example, xe2x80x9c(meth)acrylatexe2x80x9d means methacrylate or acrylate.
The first ethylenically unsaturated monomer can also be a functional monomer including for example monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto functional groups or combinations thereof. These functional monomers are generally present in the macromonomer at a level of from 0.1 weight percent to 15 weight percent and more preferably from 0.5 weight percent to 10 weight percent, and most preferably from 1.0 to 3 weight percent, based on the total weight of the graft copolymer. Used herein, all ranges are inclusive and combinable. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto-containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates; glycidylalkyl methacrylates or acrylates; or combinations thereof. Such functional monomers can provide crosslinking if desired.
The macromonomer typically also contains as polymerized units less than 10 weight percent, preferably less than 5 weight percent, more preferably less than 2 weight percent and most preferably less than 1 weight percent xe2x80x9cacid containing monomerxe2x80x9d, based on the total weight of the macromonomer. In a most preferred embodiment, the macromonomer contains no acid containing monomer. Used herein, xe2x80x9cacid containing monomerxe2x80x9d and xe2x80x9cacid functional monomerxe2x80x9d are used interchangeably. By xe2x80x9cacid containing monomerxe2x80x9d it is meant any ethylenically unsaturated monomer that contains one or more acid functional groups or functional groups that are capable of forming an acid (e.g., an anhydride such as methacrylic anhydride or tertiary butyl methacrylate). Examples of acid containing monomers include, for example, carboxylic acid bearing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid; acryloxypropionic acid and (meth)acryloxypropionic acid; sulphonic acid-bearing monomers, such as styrene sulfonic acid, sodium vinyl sulfonate, sulfoethyl acrylate, sulfoethyl methacrylate, ethylmethacrylate-2-sulphonic acid, or 2-acrylamido-2-methylpropane sulphonic acid; phosphoethylmethacrylate; the corresponding salts of the acid containing monomer; or combinations thereof.
The macromonomer may also contain as polymerized units, mercapto-olefins. Used herein, xe2x80x9cmercapto-olefinxe2x80x9d and xe2x80x9cmercaptan-olefinxe2x80x9d are used interchangeably. These mercapto-olefin compounds are those as disclosed in U.S. Pat. No. 5,247,000 to Amick. Further, the methods of U.S. Pat. No. 5,247,000 may be utilized to prepare comb copolymers of the present invention.
In a preferred embodiment of the present invention, the macromonomer is composed of 20 weight percent to 100 weight percent, more preferably from 50 to 100 weight percent, and most preferably from 70 to 100 weight percent, based on total weight of macromonomer, of at least one a-methyl vinyl monomer, a non xcex1-methyl vinyl monomer terminated with an a-methyl vinyl monomer, or combinations thereof. In a most preferred embodiment of the present invention the macromonomer contains as polymerized units from 90 to 100 weight percent xcex1-methyl vinyl monomers, non xcex1-methyl vinyl monomers terminated with xcex1-methyl vinyl monomers, or combinations thereof, based on the total weight of the macromonomer. The phrase xe2x80x9cnon xcex1-methyl vinyl monomer terminated with an xcex1-methyl vinyl monomerxe2x80x9d means that, when a vinyl monomer bearing no xcex1-methyl group is present, as polymerized units, in the macromonomer, the macromonomer must be terminated by a unit derived from an xcex1-methyl vinyl monomer. For example, while styrene might be present, as polymerized units, in a macromonomer chain, that macromonomer chain would be terminated by xcex1-methyl styrene, or some other a-methyl vinyl monomer. Suitable xcex1-methyl vinyl monomers include, for example, methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, or stearyl methacrylate; hydroxyalkyl methacrylates such as hydroxyethyl methacrylate; glycidylmethacrylate; phenyl methacrylate; methacrylamide; methacrylonitrile; or combinations thereof One skilled in the art will recognize that there are many ways to prepare the macromonomer useful in the present invention. For example, the macromonomer may be prepared by a high temperature (e.g., at least 150xc2x0 C.) continuous process such as disclosed in U.S. Pat. No. 5,710,227 or EP-A-1,010,706, published Jun. 21, 2000. In a preferred continuous process, a reaction mixture of first ethylenically unsaturated monomers is passed through a heated zone having a temperature of at least 150xc2x0 C., and more preferably at least 275xc2x0 C. The heated zone may also be maintained at a pressure above atmospheric pressure (e.g., greater than 3,000 kPa=greater than 30 bar). The reaction mixture of monomers may also optionally contain a solvent such as water, acetone, methanol, isopropanol, propionic acid, acetic acid, dimethylformamide, dimethylsulfoxide, methylethylketone, or combinations thereof.
The macromonomer useful in the present invention may also be prepared by polymerizing first ethylenically unsaturated monomers in the presence of a free radical initiator and a catalytic metal chelate chain transfer agent (e.g., a transition metal chelate). Such a polymerization may be carried out by a solution, bulk, suspension, or emulsion polymerization process. Suitable methods for preparing the macromonomer using a catalytic metal chelate chain transfer agent are disclosed in for example U.S. Pat. Nos. 4,526,945, 4,680,354, 4,886,861, 5,028,677, 5,362,826, 5,721,330, and 5,756,605; European publications EP-A-0199,436, and EP-A-0196783; and PCT publications WO 87/03605, WO 96/15158, and WO 97/34934.
Preferably, the macromonomer useful in the present invention is prepared by an aqueous emulsion free radical polymerization process using a transition metal chelate complex. Preferably, the transition metal chelate complex is a cobalt (II) or (III) chelate complex such as, for example, dioxime complexes of cobalt (II), cobalt (II) porphyrin complexes, or cobalt (II) chelates of vicinal iminohydroxyimino compounds, dihydroxyimino compounds, diazadihydroxyiminodialkyldecadienes, or diazadihydroxyiminodialkylundecadienes, or combinations thereof. These complexes may optionally include bridging groups such as BF2, and may also be optionally coordinated with ligands such as water, alcohols, ketones, and nitrogen bases such as pyridine. Additional suitable transition metal complexes are disclosed in for example U.S. Pat. Nos. 4,694,054; 5,770,665; 5,962,609; and 5,602,220. A preferred cobalt chelate complex useful in the present invention is Co II (2,3-dioxyiminobutane-BF2)2, the Co III analogue of the aforementioned compound, or combinations thereof. The spatial arrangements of such complexes are disclosed in for example EP-A-199436 and U.S. Pat. No. 5,756,605.
In preparing macromonomer by an aqueous emulsion polymerization process using a transition metal chelate chain transfer agent, at least one first ethylenically unsaturated monomer is polymerized in the presence of a free radical initiator and the transition metal chelate according to conventional aqueous emulsion polymerization techniques. Preferably, the first ethylenically unsaturated monomer is an xcex1-methyl vinyl monomer as previously described herein.
The polymerization to form the macromonomer is preferably conducted at a temperature of from 20xc2x0 C. to 150xc2x0 C., and more preferably from 40xc2x0 C. to 95xc2x0 C. The solids level at the completion of the polymerization is typically from 5 weight percent to 70 weight percent, and more preferably from 30 weight percent to 60 weight percent, based on the total weight of the aqueous emulsion.
The concentration of initiator and transition metal chelate chain transfer agent used during the polymerization process is preferably chosen to obtain the desired degree of polymerization of the macromonomer. Preferably, the concentration of initiator is from 0.2 weight percent to 3 weight percent, and more preferably from 0.5 weight percent to 1.5 weight percent, based on the total weight of monomer. Preferably, the concentration of transition metal chelate chain transfer agent is from 5 ppm to 200 ppm, and more preferably from 10 ppm to 100 ppm, based on the total monomers used to form the macromonomer.
The first ethylenically unsaturated monomer, initiator, and transition metal chelate chain transfer agent may be added in any manner known to those skilled in the art to carry out the polymerization. For example, the monomer, initiator and transition metal chelate may all be present in the aqueous emulsion at the start of the polymerization process (i.e., a batch process). Alternatively, one or more of the components may be gradually fed to an aqueous solution (i.e., a continuous or semi-batch process). For example, it may be desired to gradually feed the entire or a portion of the initiator, monomer, and/or transition metal chelate to a solution containing water and surfactant. In a preferred embodiment, at least a portion of the monomer and transition metal chelate are gradually fed during the polymerization, with the remainder of the monomer and transition metal chelate being present in the aqueous emulsion at the start of the polymerization. In this embodiment, the monomer may be fed as is, or suspended or emulsified in an aqueous solution prior to being fed.
Any suitable free radical initiator may be used to prepare the macromonomer. The initiator is preferably selected based on such parameters as its solubility in one or more of the other components (e.g., monomers, water); half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours), and stability in the presence of the transition metal chelate. Suitable initiators include for example azo compounds such as 2,2xe2x80x2-azobis (isobutyronitrile), 4,4xe2x80x2-azobis(4-cyanovaleric acid), 2,2xe2x80x2-azobis [2-methyl-N-(1,1-bis(hydroxymethyl)-2-(hydroxyethyl)]-propionamide, and 2,2xe2x80x2-azobis [2-methyl-N-(2-hydroxyethyl)]-propionamide; peroxides such as t-butyl hydroperoxide, benzoyl peroxide; sodium, potassium, or ammonium persulphate or combinations thereof. Redox initiator systems may also be used, such as for example persulphate or peroxide in combination with a reducing agent such as sodium metabisulphite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid, or combinations thereof. Metal promoters, such as iron, may also optionally be used in such redox initiator systems. Also, buffers, such as sodium bicarbonate may be used as part of the initiator system.
An emulsifier is also preferably present during the aqueous emulsion polymerization process to prepare the macromonomer. Any emulsifier may be used that is effective in emulsifying the monomers such as for example anionic, cationic, or nonionic emulsifiers. In a preferred embodiment, the emulsifier is anionic such as for example sodium, potassium, or ammonium salts of dialkylsulphosuccinates; sodium, potassium, or ammonium salts of sulphated oils; sodium, potassium, or ammonium salts of alkyl sulphonic acids, such as sodium dodecyl benzene sulfonate; sodium, potassium, or ammonium salts of alkyl sulphates, such as sodium lauryl sulfate; ethoxylated alkyl ether sulfates; alkali metal salts of sulphonic acids; C12 to C24 fatty alcohols, ethoxylated fatty acids or fatty amides; sodium, potassium, or ammonium salts of fatty acids, such as Na stearate and Na oleate; or combinations thereof. The amount of emulsifier in the aqueous emulsion is preferably from 0.05 weight percent to 10 weight percent, and more preferably from 0.3 weight percent to 3 weight percent, based on the total weight of the monomers.
The macromonomer thus prepared is emulsion polymerized with at least one second ethylenically unsaturated monomer to form a copolymer composition containing graft copolymer particles. The polymerization is carried out by providing the macromonomer as water insoluble particles in a macromonomer aqueous emulsion and the second ethylenically unsaturated monomer in a monomer composition. At least a portion of the macromonomer aqueous emulsion is combined with at least a portion of the monomer composition to form a polymerization reaction mixture that is polymerized in the presence of an initiator.
Although in no way intending to be bound by theory, it is believed that by providing the macromonomer in the form of water insoluble macromonomer particles in an aqueous emulsion, and the second ethylenically unsaturated monomer in a separate monomer composition, upon combination, the second ethylenically unsaturated monomer diffuses through the aqueous phase and then into the macromonomer particles where the polymerization occurs. Preferably, the diffusion of the second ethylenically unsaturated monomer into the macromonomer particles is evidenced by swelling of the macromonomer particles. It is an essential feature of the invention that, prior to being combined with the monomer composition, the macromonomers are present in plural discrete particles dispersed in the aqueous phase. Preferably, these plural macromonomer particles have previously been formed by aqueous emulsion polymerization, and the resultant macromonomer aqueous emulsion is combined with the monomer composition and subsequently polymerized without being isolated. Addition of the monomer composition to the macromonomer aqueous emulsion results initially in the presence of plural monomer droplets in the aqueous emulsion as separate entities distributed among, but not in direct contact with, the plural macromonomer particles. That is, the monomer droplets are separated from the macromonomer particles, and from each other, by an aqueous phase. Individual monomer molecules must then exit the monomer droplet, dissolve in the aqueous phase, diffuse through that aqueous phase to a macromonomer particle, and enter that macromonomer particle where polymerization to form the graft copolymer (i.e., comb copolymer) occurs. Because the water insoluble macromonomers are unable to diffuse through the aqueous phase, it is essential that the monomer droplets not include water insoluble macromonomer if gel formation is to be avoided and if the number of particles initially established by the macromonomer particles is to be maintained during polymerization of monomers with macromonomers.
The macromonomer aqueous emulsion useful in the present invention may be formed in any manner known to those skilled in the art. For example, the macromonomer, produced by any known method, may be isolated as a solid (e.g., spray dried) and emulsified in water. Also, for example, the macromonomer, if prepared via an emulsion or aqueous based polymerization process, may be used as is, or diluted with water or concentrated to a desired solids level.
In a preferred embodiment of the present invention, the macromonomer aqueous emulsion is formed from the emulsion polymerization of at least one first ethylenically unsaturated monomer in the presence of a transition metal chelate chain transfer agent as described previously herein. This embodiment is preferred for numerous reasons. For example, the macromonomer polymerization can be readily controlled to produce a desired particle size distribution (preferably narrow, e.g., polydispersity less than 2). Also, for example, additional processing steps, such as isolating the macromonomer as a solid, can be avoided, leading to better process economics. In addition, the macromonomer, macromonomer aqueous emulsion, and the graft copolymer can be prepared by consecutive steps in a single reactor which is desirable in a commercial manufacturing facility because process parameters, such as manufacturing cost and particle size distribution, may be optimized.
The xe2x80x9cmacromonomer aqueous emulsionxe2x80x9d useful in the present invention contains from 20 weight percent to 60 weight percent, and more preferably from 30 weight percent to 50 weight percent of at least one water insoluble macromonomer, based on the total weight of macromonomer aqueous emulsion. The macromonomer aqueous emulsion may also contain mixtures of macromonomer. Preferably, the macromonomer aqueous emulsion contains less than 5 weight percent and more preferably less than 1 weight percent of ethylenically unsaturated monomer, based on the total weight of macromonomer aqueous emulsion.
The water insoluble macromonomer particles have a particle size chosen such that, upon addition of monomers, particles of graft copolymer (i.e., comb copolymer) having a desired particle size will be formed. For example, the final graft copolymer particle size is directly proportional to the initial particle size of the macromonomer and the concentration of second ethylenically unsaturated monomer in the polymerization reaction mixture, assuming all the particles participate equally in the polymerization. Typically, the macromonomer particles, typically, have a weight average particle size of from 50 nm to 1,000 nm, preferably from 50 nm to 500 nm, and more preferably from 80 nm to 200 nm as measured by Capillary Hydrodynamic Fractionation technique using a Matec CHDF 2000 particle size analyzer equipped with a HPLC type Ultra-violet detector.
The macromonomer aqueous emulsion may also include one or more emulsifying agents. The type and amount of emulsifying agent is preferably selected in a manner to produce the desired particle size. Suitable emulsifying agents include those previously disclosed for use in preparing the macromonomer by an emulsion polymerization process. Preferred emulsifying agents are anionic surfactants such as, for example, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sulfated and ethoxylated derivatives of nonylphenols and fatty alcohols. The total level of emulsifying agent, based on the total weight of macromonomer is preferably from 0.2 weight percent to 5 weight percent and more preferably from 0.5 weight percent to 2 weight percent.
The xe2x80x9cmonomer compositionxe2x80x9d useful in the present invention contains at least one kind of second ethylenically unsaturated monomer. The monomer composition may contain all (i.e., 100%) monomer, or contain monomer dissolved or dispersed in an organic solvent and/or water. Preferably, the level of monomer in the monomer composition is from 50 weight percent to 100 weight percent, more preferably from 60 to 90 weight percent, and most preferably from 70 to 80 weight percent, based on the total weight of the monomer composition. Examples of organic solvents that may be present in the monomer composition include C6 to C14 alkanes. The organic solvent in the monomer composition will be no more than 30 weight percent, and more preferably no more than 5 weight percent, based on the total weight of the monomer composition.
In addition to water and/or organic solvent, the monomer composition may also optionally contain monomers containing functional groups, such as, for example, monomers containing hydroxy, amido, aldehyde, ureido, polyether, glycidylalkyl, keto groups or combinations thereof. These other monomers are generally present r. the monomer composition at a level of from 0.5 weight percent to 15 weight percent, and more preferably from 1 weight percent to 3 weight percent based on the total weight of the graft copolymer. Examples of functional monomers include ketofunctional monomers such as the acetoacetoxy esters of hydroxyalkyl acrylates and methacrylates (e.g., acetoacetoxyethyl methacrylate) and keto-containing amides (e.g., diacetone acrylamide); allyl alkyl methacrylates or acrylates; glycidylalkyl methacrylates or acrylates; or combinations thereof Such functional monomer can provide crosslinking if desired.
In a preferred embodiment, the monomers in the monomer composition are pre-emulsified in water to form a xe2x80x9cmonomer aqueous emulsionxe2x80x9d. Preferably, the monomer aqueous emulsion contains monomer droplets having a droplet size from 1 micron to 100 microns, and more preferably from 5 micron to 50 microns. Any suitable emulsifying agent may be used, for example those previously described, to emulsify the monomer to the desired monomer droplet size. Preferably, the level of emulsifying agent, if present, will be from 0.2 weight percent to 2 weight percent based on the total weight of monomer in the monomer composition.
The second ethylenically unsaturated monomer of the monomer composition is preferably selected to provide the desired properties in the resulting comb copolymer composition. Preferably, the second ethylenically unsaturated monomers are chosen so that, when they have been polymerized to form the backbone of the comb copolymer, that backbone will preferably have a Tg of xe2x88x9265xc2x0 C. to 10xc2x0 C., more preferably xe2x88x9245xc2x0 C. to 10xc2x0 C., and most preferably xe2x88x9240xc2x0 C. to 0xc2x0 C., estimated as described herein above. Suitable ethylenically unsaturated monomers include for example methacrylate esters, such as C1 to C18 normal or branched alkyl esters of methacrylic acid, including methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, isobornyl methacrylate; acrylate esters, such as C1 to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, a-methyl styrene or t-butyl styrene; olefinically unsaturated nitriles, such as acrylonitrile or methacrylonitrile; olefinically unsaturated halides, such as vinyl chloride, vinylidene chloride or vinyl fluoride; vinyl esters of organic acids, such as vinyl acetate; N-vinyl compounds such as N-vinyl pyrrolidone; acrylamide; methacrylamide; substituted acrylamides; substituted methacrylamides; hydroxyalkylmethacrylates such as hydroxyethylmethacrylate; hydroxyalkylacrylates; dienes such as 1,3-butadiene and isoprene; vinyl ethers; or combinations thereof. The ethylenically unsaturated monomer can also be an acid containing monomer or a functional monomer, such as those previously described herein. Preferably, the ethylenically unsaturated monomer of the monomer composition does not contain amino groups.
In a preferred embodiment, the monomer composition includes one or more ethylenically unsaturated monomers selected from Cl to C18 normal or branched alkyl esters of acrylic acid, including methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate; styrene; substituted styrenes, such as methyl styrene, xcex1-methyl styrene or t-butyl styrene; butadiene or combinations thereof.
As previously mentioned, the macromonomer aqueous emulsion and monomer composition are combined to form a xe2x80x9cpolymerization reaction mixturexe2x80x9d, and polymerized in the presence of a free radical initiator to form an xe2x80x9caqueous copolymer compositionxe2x80x9d, also referred to herein as an xe2x80x9caqueous dispersion of a segmental copolymerxe2x80x9d. The term xe2x80x9cpolymerization reaction mixture,xe2x80x9d as used herein, refers to the resulting mixture formed when at least a portion of the macromonomer aqueous emulsion and at least a portion of the monomer composition are combined. The polymerization reaction mixture may also contain initiator or any other additive used during the polymerization. Thus, the polymerization reaction mixture is a mixture that changes in composition as the macromonomer and monomer (i.e., second ethylenically unsaturated monomer) of the monomer composition are reacted to form comb copolymer.
The macromonomer aqueous emulsion and monomer composition may be combined in various ways to carry out the polymerization. For example, the macromonomer aqueous emulsion and the monomer composition may be combined prior to the start of the polymerization reaction to form the polymerization reaction mixture. Alternatively, the monomer composition could be gradually fed into the macromonomer aqueous emulsion, or the macromonomer aqueous emulsion could be gradually fed into the monomer composition. It is also possible that only a portion of the macromonomer aqueous emulsion and/or monomer composition be combined prior to the start of the polymerization with the remaining monomer composition and/or macromonomer aqueous emulsion being fed during the polymerization.
The initiator can also be added in various ways. For example, the initiator may be added in xe2x80x9cone shotxe2x80x9d to the macromonomer aqueous emulsion, the monomer composition, or a mixture of the macromonomer aqueous emulsion and the monomer composition at the start of the polymerization. Alternatively, all or a portion of the initiator can be co-fed as a separate feed stream, as part of the macromonomer aqueous emulsion, as part of the monomer composition, or any combination of these methods.
The preferred method of combining the macromonomer aqueous emulsion, the monomer composition, and initiator will depend on such factors as the desired graft copolymer composition. For example, the distribution of the macromonomer as a graft along the backbone can be affected by the concentrations of both the macromonomer and the second ethylenically unsaturated monomers at the time of the polymerization. In this regard, a batch process will afford high concentration of both the macromonomer and the second ethylenically unsaturated monomers at the onset of the polymerization whereas a semi-continuous process will keep the second ethylenically unsaturated monomer concentration low during the polymerization. Thus, through the method by which the macromonomer aqueous emulsion and monomer composition are combined, it is possible to control, for example: the number of graft segments, derived from macromonomer, per polymer chain; the distribution of graft segments in each chain, and the length of the polymer backbone.
Initiators useful in polymerizing the macromonomer and second ethylenically unsaturated monomer include any suitable initiator for emulsion polymerizations known to those skilled in the art. The selection of the initiator will depend on such factors as the initiator""s solubility in one or more of the reaction components (e.g. monomer, macromonomer, water); and half life at the desired polymerization temperature (preferably a half life within the range of from about 30 minutes to about 10 hours). Suitable initiators include those previously described herein in connection with forming the macromonomer, such as azo compounds such as 4,4xe2x80x2-azobis(4-cyanovaleric acid), peroxides such as t-butyl hydroperoxide; sodium, potassium, or ammonium persulfate; redox initiator systems such as, for example, persulphate or peroxide in combination with a reducing agent such as sodium metabisulfite, sodium bisulfite, sodium formaldehyde sulfoxylate, isoascorbic acid; or combinations thereof. Metal promoters, such as iron; and buffers, such as sodium bicarbonate, may also be used in combination with the initiator. Additionally, Controlled Free Radical Polymerization (CFRP) methods such as Atom Transfer Radical Polymerization; or Nitroxide Mediated Radical Polymerization may be used. Preferred initiators include azo compounds such as 4,4xe2x80x2-azobis(4-cyanovaleric acid).
The amount of initiator used will depend on such factors as the copolymer desired and the initiator selected. Preferably, from 0.1 weight percent to 1 weight percent initiator is used, based on the total weight of monomer and macromonomer.
The polymerization temperature will depend on the type of initiator chosen and desired polymerization rates. Preferably, however, the macromonomer and second ethylenically unsaturated monomer are polymerized at a temperature of from 0xc2x0 C. to 150xc2x0 C., and more preferably from 20xc2x0 C. to 95xc2x0 C.
The amount of macromonomer aqueous emulsion and monomer composition added to form the polymerization reaction mixture will depend on such factors as the concentrations of macromonomer and second ethylenically unsaturated monomer in the macromonomer aqueous emulsion and monomer composition, respectively, and the desired comb copolymer composition. Preferably, the macromonomer aqueous emulsion and monomer composition are added in amounts to provide a comb copolymer containing as polymerized units from 50 weight percent to 70 weight percent, and more preferably from 55 weight percent to 65 weight percent second ethylenically unsaturated monomer.
One skilled in the art will recognize that other components used in conventional emulsion polymerizations may optionally be used in the method of the present invention. For example, to reduce the molecular weight of the resulting graft copolymer, the polymerization may optionally be conducted in the presence of one or more chain transfer agents, such as n-dodecyl mercaptan, thiophenol; halogen compounds such as bromotrichloromethane; or combinations thereof. Also, additional initiator and/or catalyst may be added to the polymerization reaction mixture at the completion of the polymerization reaction to reduce any residual monomer, (e.g., chasing agents). Suitable initiators or catalysts include those initiators previously described herein. In addition, the chain transfer capacity of a macromonomer through addition-fragmentation can be utilized in part to reduce molecular weight through appropriate design of monomer compositions and polymerization conditions. See e.g., E. Rizzardo, et. al., Prog. Pacific Polym. Sci., 1991, 1, 77-88; G. Moad, et. al., WO 96/15157.
Preferably, the process of the present invention does not require neutralization of the monomer, or resulting aqueous graft copolymer composition. These components preferably remain in unneutralized form (e.g., no neutralization with a base if acid functional groups are present).
The resulting aqueous graft copolymer composition formed by polymerization of the macromonomer and the ethylenically unsaturated monomer in the monomer composition preferably has a solids level of from 30 weight percent to 70 weight percent and more preferably from 40 weight percent to 60 weight percent. The aqueous graft copolymer composition typically contains graft copolymer particles that are water insoluble and have a particle size of from, 60 nm to 1,000 nm, preferably from 60 nm to 500 nm, and more preferably from 80 nm to 350 nm.
The graft copolymer formed preferably has a backbone containing, as polymerized units, the second ethylenically unsaturated monomer from the monomer composition, and one or more macromonomer units, as polymerized units, wherein a terminal ethylenically unsaturated group of the macromonomer is incorporated into the backbone and the remainder of the macromonomer becomes a graft segment pendant to the backbone (i.e., a side chain) upon polymerization. Preferably, each side chain is a graft segment derived from the grafting of one macromonomer to the backbone. The degree of polymerization of the graft segments derived from the macromonomer is preferably from 10 to 1,000, more preferably from 20 to 1,000, and most preferably from 40 to 200, where the degree of polymerization is expressed as the number of polymerized units of ethylenically unsaturated monomer used to form the macromonomer. The weight average molecular weight of the graft copolymer (i.e., of the comb copolymer) is preferably in the range of from 80,000 to 2,000,000, and more preferably from 100,000 to 1,000,000. The number average molecular weight of a comb copolymer is typically less than the corresponding weight average molecular weight. The number average molecular weights of the comb copolymers of the present invention are at least 25,000, and typically range from 25,000 to 600,000. Weight average molecular weights as used herein can be determined by size exclusion chromatography.
The comb copolymer particles of the aqueous graft copolymer composition can be isolated, for example, by spray drying or coagulation.
In a preferred embodiment of the present invention, the polymerization is conducted in two stages. In the first stage, the macromonomer is formed in an aqueous emulsion polymerization process, and in the second stage the macromonomer is polymerized with the second ethylenically unsaturated monomer in an emulsion. For efficiency, preferably these two stages are conducted in a single vessel. For example, in the first stage, the macromonomer aqueous emulsion may be formed by polymerizing in an aqueous emulsion at least one first ethylenically unsaturated monomer to form water insoluble macromonomer particles. This first stage polymerization is preferably conducted using a transition metal chelate chain transfer agent as previously described herein. After forming the macromonomer aqueous emulsion, a second emulsion polymerization is preferably performed in the same vessel to polymerize the macromonomer with at least one second ethylenically unsaturated monomer. This second stage may be conducted for example by directly adding (e.g., all at once or by a gradual feed) the monomer composition and initiator to the macromonomer aqueous emulsion. One main advantage of this embodiment is that the macromonomer does not have to be isolated, and the second polymerization can take place simply by adding the monomer composition and initiator to the macromonomer aqueous emulsion. In this preferred embodiment, the particle size and particle size distribution of the plural water insoluble macromonomer particles may be precisely controlled, and later addition of more macromonomer aqueous emulsion would typically not be required, except when, for example, a second mode (particle size and/or composition) of graft copolymer is desired.
In another preferred embodiment of the present invention, the polymerization of the macromonomer and second ethylenically unsaturated monomer is at least partially performed in the presence of an acid containing monomer, acid containing macromonomer, or combinations thereof. The acid containing monomer or acid containing macromonomer may be added in any manner to the polymerization reaction mixture. Preferably, the acid containing monomer or acid containing macromonomer is present in the monomer composition. The acid containing monomer or acid containing macromonomer may also be added as a separate stream to the polymerization reaction mixture.
The amount of acid containing monomer or acid containing macromonomer added to the polymerization reaction mixture is typically from 0 to 10 weight percent, preferably from 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent, based on the total weight of monomer and macromonomer added to the polymerization reaction mixture.
Acid containing monomers which may be used in this embodiment include ethylenically unsaturated monomers bearing acid functional or acid forming groups such as those previously described herein. The xe2x80x9cacid containing macromonomerxe2x80x9d useful in this embodiment is any low molecular weight polymer having at least one terminal ethylenically unsaturated group that is capable of being polymerized in a free radical polymerization process, and that is formed from at least one kind of acid containing monomer. Preferably, the amount of acid containing monomer present, as polymerized units, in the acid containing macromonomer is from 50 weight percent to 100 weight percent, more preferably from 90 weight percent to 100 weight percent, and most preferably from 95 weight percent to 100 weight percent.
The acid containing macromonomer may be prepared according to any technique known to those skilled in the art such as those previously described herein. In a preferred embodiment of the present invention, the acid containing macromonomer is prepared by a solution polymerization process using a free radical initiator and transition metal chelate complex. Such a process is disclosed in, for example, U.S. Pat. No. 5,721,330. Preferred acid containing monomers used to form the acid containing macromonomer are xcex1-methyl vinyl monomers such as methacrylic acid.
In another preferred embodiment of the present invention, a xe2x80x9cmacromolecular organic compoundxe2x80x9d having a hydrophobic cavity is present in the polymerization medium used to form the macromonomer and/or aqueous copolymer composition. Typically, the macromolecular organic compound may be used whenever facilitation of transport of monomer, or other ingredient, through the aqueous phase is needed. In this way, even the aqueous phase transport of monomers having low to moderate water solubility may be facilitated. Preferably, the macromolecular organic compound is used when the momomer to be transported has a water solubility no greater than 150 millimoles/liter. More preferably, the macromolecular organic compound is used when copolymerizing ethylenically unsaturated monomers with very low water solubility such as lauryl or stearyl acrylates and/or methacrylates. By xe2x80x9cvery low water solubilityxe2x80x9d it is meant a water solubility at 25xc2x0 C. to 50xc2x0 C. of no greater than 50 millimoles/liter. For example, the macromolecular organic compound may be added to the monomer composition, the macromonomer aqueous emulsion, or the polymerization reaction mixture used to form the aqueous copolymer composition. Also, for example, the macromolecular organic compound may be added to an aqueous emulsion of ethylenically unsaturated monomer used to form the macromonomer. Suitable techniques for using a macromolecular organic compound having a hydrophobic cavity are disclosed in, for example, U.S. Pat. No. 5,521,266.
Preferably, the macromolecular organic compound having a hydrophobic cavity is added to the polymerization reaction mixture to provide a molar ratio of macromolecular organic compound to very low water solubility monomer or macromonomer of from 5:1 to 1:5000 and more preferably from 1:1 to 1:500.
Macromolecular organic compounds having a hydrophobic cavity useful in the present invention include for example cyclodextrin or cyclodextrin derivatives; cyclic oligosaccharides having a hydrophobic cavity such as cycloinulohexose, cycloinuloheptose, or cycloinuloctose; calyxarenes; cavitands; or combinations thereof. Preferably, the macromolecular organic compound is xcex2-cyclodextrin, more preferably methyl-xcex2-cyclodextrin.
Monomers having low water solubility include for example primary alkenes; styrene and alkylsubstituted styrene; xcex1-methyl styrene; vinyltoluene; vinyl esters of C4 to C30 carboxylic acids, such as vinyl 2-ethylhexanoate, vinyl neodecanoate; vinyl chloride; vinylidene chloride; N-alkyl substituted (meth)acrylamide such as octyl acrylamide and maleic acid amide; vinyl alkyl or aryl ethers with (C3-C30) alkyl groups such as stearyl vinyl ether; (C1-C30) alkyl esters of (meth)acrylic acid, such as methyl methacrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate; unsaturated vinyl esters of (meth)acrylic acid such as those derived from fatty acids and fatty alcohols; multifunctional monomers such as pentaerythritol triacrylate; monomers derived from cholesterol or combinations thereof.
In another aspect of the present invention an aqueous copolymer composition is provided that is preferably produced by the method of the present invention as previously described herein. The aqueous copolymer composition contains a plurality of water insoluble particles of comb copolymer. The comb copolymer particles preferably have a weight average particle size of from 60 nm to 1,000 nm, more preferably from 60 nm to 500 nm, and most preferably from 80 nm to 350 nm.
The second ethylenically unsaturated monomer may be any ethylenically unsaturated monomer that provides desirable properties in the copolymer particles, such as those useful in the monomer composition as previously described herein.
The weight ratio of graft segment to backbone of the comb copolymer of the present invention is preferably 30:70 to 60:40, more preferably 35:65 to 50:50, and most preferably 35:65 to 45:55.
Although the backbone of the comb copolymer may be branched, with such branching including, for example, xe2x80x9cstarxe2x80x9d structures, it is preferred that the backbone is linear. Compositionally, the backbone of the copolymer preferably contains polymerized units of the second ethylenically unsaturated monomer derived from the monomer composition.
Preferably, the Tg of the backbone is from xe2x88x9265xc2x0 C. to 10xc2x0 C., more preferably from xe2x88x9245xc2x0 C. to 10xc2x0 C., and most preferably from xe2x88x9240xc2x0 C. to 0xc2x0 C.
The pendant graft segments of the comb copolymer preferably contain polymerized units of the macromonomer. In a preferred embodiment of the present invention, each graft segment is derived from one macromonomer. Additionally, the pendant graft segments contain less than 5 weight percent and more preferably less than 1 weight percent of the polymerized second ethylenically unsaturated monomer derived from the monomer composition, based on the total weight of the pendant graft segments.
Preferably, the Tg of the graft segment of the comb copolymer is from 60xc2x0 C. to 180xc2x0 C., more preferably from 70xc2x0 C. to 130xc2x0 C., and most preferably from 80xc2x0 C. to 120xc2x0 C.
It is further preferred that the graft segment is miscible with the substrate polymer of the present invention. Although not wishing to be bound be any particular theory, it is thought that this miscibility of the graft segment is desirable because favorable interaction of the graft segment with the substrate polymer enhances adhesion between the capstock layer and the layer of substrate polymer. The solubility parameters of the graft segment and the substrate polymer can be estimated and compared to predict miscibility by methods such as that of Van Krevelen, described herein above.
In a preferred embodiment of the present invention, the water insoluble comb copolymer particles typically contain from 0 weight percent to 10 weight percent, preferably 0.2 weight percent to 10 weight percent, more preferably from 0.5 weight percent to 5 weight percent, and most preferably from 1 weight percent to 2 weight percent of an acid containing macromonomer, based on the total weight of the graft copolymer. The acid containing macromonomer preferably has a composition as previously described herein.
Although in no way intending to be bound by theory, it is believed that the xe2x80x9cacid containing macromonomerxe2x80x9d is attached to the surface of the water insoluble graft copolymer particles and provides stability. By xe2x80x9cattached,xe2x80x9d as used herein, it is believed that the acid containing macromonomer is bound in some manner (e.g., covalent, hydrogen bonding, ionic) to a polymer chain in the particle. Preferably, the acid containing macromonomer is covalently bound to a polymer chain in the particle. It has been found that the acid containing macromonomer provides stability to the particles such that the aqueous copolymer composition produced exhibits unexpected improved shear stability; freeze thaw stability; and stability to additives in formulations, as well as reduction of coagulum during the polymerization. Although improved stability can be achieved using acid containing monomer, these benefits are most dramatic when an acid containing macromonomer is used.
The aqueous copolymer composition in addition to the copolymer particles preferably contains less than 10 weight percent, and more preferably less than 1 weight percent of organic solvent. In a most preferred embodiment, the aqueous copolymer composition contains no organic solvent.
An advantage of using the method of the present invention to prepare the aqueous copolymer composition is that the resulting copolymer composition contains low levels of homopolymer, such as for example homopolymer of second ethylenically unsaturated monomer derived from the monomer composition or homopolymer of macromonomer derived from the macromonomer aqueous emulsion. Preferably the aqueous copolymer composition contains less than 30 weight percent and more preferably less than 20 weight percent of homopolymer of macromonomer, based on the total weight of the graft copolymer. Preferably also the aqueous copolymer composition contains less than 30 weight percent and more preferably less than 20 weight percent of homopolymer of second ethylenically unsaturated monomer.
The comb copolymer of the present invention may be isolated as powders, or other solid particles, from dispersions containing it (e.g., aqueous emulsions) by methods well known in the art. These methods include, for example, spray drying, coagulation and oven drying, freeze drying, and devolatilizing extrusion.
The substrate composition and, hence, the substrate layer of the present invention may include any thermoplastic polymer known to the art. Preferably, the thermoplastic polymer is a polymer selected from the group consisting of poly(vinyl halide), chlorinated poly(vinyl chloride), ABS terpolymer, polyaromatics including high impact polystyrene (HIPS), polyamides, polyesters, polyolefins including polypropylene, and combinations thereof. More preferably, the thermoplastic polymer is a polymer selected from the group consisting of poly(vinyl chloride), ABS terpolymer, and combinations thereof. Most preferably, the thermoplastic polymer is poly(vinyl chloride). The acronyms in parentheses above are the ASTM D4000 acronyms.
The term xe2x80x9cpoly(vinyl halide)xe2x80x9d is used generically herein to define not only poly(vinyl chloride), but also analogous polymers, such as poly(vinyl bromide), and chlorinated polyvinyl chloride; poly(vinylidene chloride) and its derivatives, including poly(vinylidene chloride-vinyl acetate); and vinyl chloride copolymers or terpolymers having vinyl chloride as the major component (greater than 50% by weight). These copolymers and terpolymers include, as polymerized units, comonomers of vinyl alkanoates such as vinyl acetate; vinylidene halides such as vinylidene chloride; alkyl esters of carboxylic acids such as acrylic acid, ethyl acrylate, and 2-ethylhexyl acrylate; unsaturated hydrocarbons such as ethylene, propylene, and isobutylene; and, allyl compounds, such as allyl acetate.
The term xe2x80x9cABS terpolymerxe2x80x9d is used generically herein not only to define a terpolymer of acrylonitrile, butadiene, and styrene, but also analogous polymers in which the ABS comonomers have been replaced in whole or in part by analogous comonomers, as polymerized units. For example, acrylonitrile is replaced by, or supplemented with methacrylonitrile, ethacrylonitrile, or halogenated acrylonitriles; styrene is replaced by, or supplemented with alpha-methyl styrene, chlorostyrene, or vinyl toluene; butadiene is replaced by, or supplemented with isoprene.
The xe2x80x9csolid capstock layerxe2x80x9d of the present invention can be prepared by forming and melt processing a xe2x80x9ccapstock compositionxe2x80x9d. The capstock composition includes a comb copolymer. The comb copolymer may be melt processed as is, or in combination with additives as are described herein below. If additives are included, they may be combined with the comb copolymer by blending methods well known to those skilled in the art. For example, a Henschel Blender (available from Henschel Mixers Americas, Houston, Tex.), may be used to blend the comb copolymer with additives, including, for example, other comb copolymers. Hand blending (e.g., by shaking the components of the capstock composition in a bag) may also be employed, as may be pre-extrusion to form pellets.
The capstock composition is then, typically, fed to the feed section of a first extruder. The screw or screws (e.g., of single or twin-screw extruders, respectively) of the first extruder then convey the capstock composition to the metering section where mixing and heating occur to form a xe2x80x9ccapstock meltxe2x80x9d. The metering section of the extruder may have multiple zones and may also have multiple screw sections, each having a different design. The capstock melt is maintained at a temperature above the temperature at which it becomes fluid and below the temperature at which significant decomposition would occur before the capstock melt could exit the first extruder. The optimum melt temperature will, of course, vary according to the capstock composition being mixed and heated. Typically, this melt temperature will be between 100xc2x0 C. and 250xc2x0 C.
The capstock melt is then conveyed to a die where it is formed into a xe2x80x9ccapstock melt layerxe2x80x9d which is, in turn, extruded through the exit opening of the die. The capstock melt layer is cooled by air or other cooling fluid as it exits the die. Often the die itself is cooled by a cooling fluid (e.g., water, or oil) so that cooling of the capstock melt begins within the die block. The cooling of the capstock melt layer converts it to a xe2x80x9csolid capstock layerxe2x80x9d which is the capstock layer of the multi-layer polymeric composite. The thickness of the capstock layer may be several millimeters, but is, preferably 10 to 1,000 microns, more preferably 25 to 500 microns, and most preferably, 25 to 250 microns.
The xe2x80x9csolid substrate layerxe2x80x9d of the present invention is formed in a manner similar to that used to form the capstock layer, beginning with the formation of a xe2x80x9csubstrate compositionxe2x80x9d which includes a thermoplastic polymer, and may include additives such as are described herein below. The substrate composition is then, typically, fed to the feed section of a second extruder. The screw or screws of the second extruder then convey the substrate composition to the metering section where mixing and heating occur to form a xe2x80x9csubstrate meltxe2x80x9d. The metering section of the extruder may have multiple zones and may also have multiple screw sections, each having a different design. The substrate melt is maintained at a temperature above the temperature at which it becomes fluid and below the temperature at which significant decomposition would occur before the substrate melt could exit the second extruder. The optimum melt temperature will, of course, vary according to the substrate composition being mixed and heated. Typically, this melt temperature of the substrate melt will be between 100xc2x0 C. and 350xc2x0 C. For example, the processing temperature for melts of poly(vinyl chloride) is characteristically in the range of 185xc2x0 C. to 205xc2x0 C.
The substrate melt is then conveyed to a die where it is formed into a xe2x80x9csubstrate melt layerxe2x80x9d which is, in turn, extruded through the exit opening of the die of the second extruder. The substrate melt layer is cooled by air or other cooling fluid as it exits the die. Often the die itself is cooled by a cooling fluid (e.g., water, or oil) so that cooling of the substrate melt begins within the die block. The cooling of the substrate melt layer converts it to a xe2x80x9csolid substrate layerxe2x80x9d which is the substrate layer of the multi-layer polymeric composite. The thickness of the substrate layer is, preferably 10 to 1,000 microns, more preferably 25 to 500 microns, and most preferably, 25 to 250 microns.
Typically, the first and second extruder are arranged so that their extruder barrels converge such that their die areas are in intimate contact, thereby allowing the capstock melt layer to contact the substrate melt layer as those melt layers exit their respective dies. In this way, the capstock melt layer becomes disposed upon the substrate melt layer, adhering thereto, thereby forming a xe2x80x9cmulti-layered melt compositexe2x80x9d. As the capstock melt layer and substrate melt layer cool, they form the solid capstock layer and the solid substrate layer of the multi-layered polymeric composite of the present invention. Co-extruders may include more than two extruders, and multi-layered polymeric composites having more than two layers may be prepared by the method of the present invention. The multi-layered composite so formed may include more than one substrate layer, or even more than one capstock layer.
In addition to co-extrusion, multi-layered polymeric composites may be prepared using, for example, presses, molds, injection molds, and blow molds. Any type of thermoplastic article common to the art may be made by the method of the present invention. A non-exhaustive list of these articles includes, for example: construction materials, such as siding, pipe, wallboard, wall-covering, and window frame; films and laminates; appliance housings such as housings for computers, refrigerators, and air conditioners; both interior and exterior automotive parts; packaging materials; and toys.
Certain lubricants, stabilizers, and the like are often incorporated into the capstock composition, and hence the capstock melt layer and the solid capstock layer. The stabilizers serve to prevent the breakdown of the thermoplastic polymer and are of several different types. Two varieties stabilize against thermal and ultraviolet light stimulated oxidative degradation, mechanical degradation, and discoloration.
Other additives to the capstock composition, and capstock melt layer and solid capstock layer, prepared in accordance with the present invention may include, for example: colorants, including organic dyes, such as anthraquinone red, organic pigments such as phthalocyanine blue, and inorganic pigments such as titanium dioxide, zinc oxide, and cadmium sulfide. Polymeric or inorganic fillers and particulate extenders can be added to reduce cost and reduce gloss. Examples are carbon black, amorphous silica, asbestos, talc, calcium carbonate, magnesium carbonate, clays, and glass or carbon fibers. Large particle size polymeric matting or flattening agents may be added. The capstock composition may include more than one type of comb copolymer. The capstock composition may also include thermoplastic polymers compatible with the comb copolymer. Compatible thermoplastic polymer include, for example acrylic, poly(vinyl chloride), and vinylidene fluoride copolymer. It may further include other impact modifiers, such as typical crosslinked core/shell poly(butadiene/styrene)/poly(methacrylate) modifiers and crosslinked poly(butyl acrylate)/poly(methacrylate).
All of the additives just enumerated, may, optionally, be included in the substrate composition, and hence the substrate melt layer and solid substrate layer, of the present invention.
While only a few of such materials have been specifically recited, it is not intended to exclude others; the recitation is exemplary only, and each category of additives is common and well-known in the art. The inclusions can be made at any stage of preparation in accordance with accepted techniques well-known to those ordinarily skilled in the art, in proportions which are commonly employed. Such additional materials are not of particular significance in the present invention.
Experimental
Molecular Weight Determination Using Gel Permeation Chromatography (GPC)
Gel Permeation Chromatography, otherwise known as size exclusion chromatography, actually separates the members of a distribution of polymer chains according to their hydrodynamic size in solution rather than their molar mass. The system is then calibrated with standards of known molecular weight and composition to correlate elution time with molecular weight. The techniques of GPC are discussed in detail in Modern Size Exclusion Chromatography, W. W. Yau, J. J Kirkland, D. D. Bly; Wiley-Interscience, 1979, and in A Guide to Materials Characterization and Chemical Analysis, J. P. Sibilia; VCH, 1988, p.81-84.
For example, the molecular weight information for a low molecular weight sample (e.g., 10,000) may be determined as follows: The sample (an aqueous emulsion containing low molecular weight particles) is dissolved in THF at a concentration of approximately 0.1% weight sample per volume THF, and shaken for 6 hours, followed by filtration through a 0.45 xcexcm PTFE (polytetrafluoroethylene) membrane filter. The analysis is performed by injecting 100 xcexcl of the above solution onto 3 columns, connected in sequence and held at 40xc2x0 C. The three columns are: one each of PL Gel 5 100, PL Gel 5 1,000, and PL Gel 5 10,000, all available from Polymer Labs, Amherst, Mass. The mobile phase used is THF flowing at 1 ml/min. Detection is via differential refractive index. The system was calibrated with narrow polystyrene standards. PMMA-equivalent molecular weights for the sample are calculated via Mark-Houwink correction using K=14.1xc3x9710xe2x88x923 ml/g and a=0.70 for the polystyrene standards and K=10.4xc3x9710xe2x88x923 ml/g and a=0.697 for the sample.